As it has been well known that prostate carcinoma (hereinafter abbreviated as “Pca”) is one of the leading causes of death of males, and a prostate-specific antigen (hereinafter abbreviated as “PSA”) has been recognized as the most important tumor marker for Pca (Nonpatent Document 1). PSA is a glycoprotein of about 34 kDa and contains glycans in a proportion of about 8% thereof. The usefulness of a serum PSA test for the early diagnosis of Pca has already been described in many literatures. However, there is a region between males affected with Pca and males affected with benign prostate hyperplasia (hereinafter, abbreviated as “BPH”) called a gray zone where Pca and BPH cannot be distinguished (Nonpatent Document 2). Therefore, attempts to accurately distinguish between these two pathologies, for example, attempts using a PSA density, a PSA gradient, the ratio of free PSA/total PSA, or the like as an index have been made. However, it is difficult to accurately distinguish between these two pathologies using such a method. Accordingly, the fact that a current serum PSA test is not specific to Pca and also does not have an appropriate cutoff value which satisfies both sensitivity and specificity has become a worldwide problem.
Under such a circumstance, a group including Ohyama, who is one of the present inventors, and others identified 19 types of glycans of PSA by treating PSA purified from seminal vesicle fluid with N-Glycosidase F, cleaving N-type glycans of PSA, and carrying out an analysis by matrix associated laser desorption/ionization time-of-flight (MALDI TOF) mass spectrometry (MS), and revealed that the glycans of PSA are very rich in diversity (Nonpatent Document 3). Prior to that, a group including Stamey and others has reported that as glycans of PSA, only an N-type glycan, which is composed of two strands, and in which sialic acid is bound at the terminal to galactose through an α(2,6) bond, is expressed (Nonpatent Document 4). However, it was revealed by the group including Ohyama and others that a glycan in which terminal sialic acid is bound to galactose through an α(2,3) bond is also present in a proportion of about 10% as well as a glycan in which terminal sialic acid is bound to galactose through an α(2,6) bond. After that, the group including Ohyama and others revealed that by analyzing PSA not only in a state of only glycans, but also in a state including a peptide sequence of PSA by MS-MS, a terminal sialic acid residue of an N-type glycan of PSA which is bound to galactose through an α(2,3) bond rather than through an α(2,6) bond increases with malignant transformation (Nonpatent Document 5).
In view of the above findings, it is considered that Pca and BPH can be distinguished from each other by using the amount of PSA having an N-type glycan in which a terminal sialic acid residue is bound to galactose through an α(2,3) bond as an index. In fact, it has been confirmed that Pca and BPH can be distinguished from each other by affinity chromatography using Maackia amurensis lectin capable of specifically recognizing a glycan in which a terminal sialic acid residue is bound to galactose through an α(2,3) bond, which has been proposed in Patent Document 1 by Ohyama who is one of the present inventors. The method for distinguishing between Pca and BPH by affinity chromatography using Maackia amurensis lectin has drawn attention as a method completely different from the methods which have been proposed so far. However, the method has a problem that a large amount (about 10 mL) of serum is required as an analyte sample for carrying out highly accurate discrimination because the amount of PSA having an N-type glycan in which a terminal sialic acid residue is bound to galactose through an α(2,3) bond is extremely small and is only 1 to 2% of the total PSA amount. Further, since Maackia amurensis lectin to be used is an extract from a natural product, the method also has a problem that a variation in quality is observed among lots.